An electrophotographic light-sensitive material may have various structures depending upon the characteristics required or an electrophotographic process to be employed.
An electrophotographic system in which the light-sensitive material comprises a support having thereon at least one photoconductive layer and, if necessary, an insulating layer on the surface thereof is widely employed. The electrophotographic light-sensitive material comprising a support and at least one photoconductive layer formed thereon is used for the image formation by an ordinary electrophotographic process including electrostatic charging, imagewise exposure, development, and, if desired, transfer.
Furthermore, a process using an electrophotographic light-sensitive material as an offset master plate precursor for direct plate making is widely practiced.
Binders which are used for forming the photoconductive layer of an electrophotographic light-sensitive material are required to be excellent in the film-forming properties by themselves and the capability of dispersing photoconductive powder therein. Also, the photoconductive layer formed using the binder is required to have satisfactory adhesion to a base material or support. Further, the photoconductive layer formed by using the binder is required to have various excellent electrostatic characteristics such as high charging capacity, small dark decay, large light decay, and less fatigue due to prior light-exposure and also have an excellent image forming properties, and the photoconductive layer stably maintains these electrostatic characteristics regardless of change of humidity at the time of image formation.
Further, extensive investigations have been made on lithographic printing plate precursors using an electrophotographic light-sensitive material, and for such a purpose, binder resins for a photoconductive layer which satisfy both the electrostatic characteristics as an electrophotographic light-sensitive material and printing properties as a printing plate precursor are required.
However, conventional binder resins used for electrophotographic light-sensitive materials have various problems particularly in electrostatic characteristics such as a charging property, dark charge retention and photosensitivity, and smoothness of the photoconductive layer.
Also, binder resins which have been developed for lithographic printing master plate by an electrophotographic system have been found, upon practical evaluations, that they have also problems in the above-described electrostatic characteristics, background staining of prints, etc.
In order to overcome these problems, JP-A-63-217354 and JP-A-1-70761 (the term "JP-A" as used herein means an "unexamined Japanese patent application") disclose improvements in the smoothness of the photoconductive layer and electrostatic characteristics by using, as a binder resin, a resin containing from 0.05 to 10% by weight of a copolymer having an acidic group in a side chain of the polymer or a resin having a weight average molecular weight of from 1.times.10.sup.3 to 1.times.10.sup.4 and having an acidic group bonded at only one terminal of the polymer main chain thereby obtaining an image having no background stains.
Also, JP-A-1-100554 and JP-A-1-214865 disclose a technique using, as a binder resin, a resin containing an acidic group in a side chain of the copolymer or at the terminal of the polymer main chain, and containing a polymerizable component having a heat- and/or photo-curable functional group; JP-A-1-102573 and JP-A-2-874 disclose a technique using a resin containing an acidic group in a side chain of the copolymer or at the terminal of the polymer main chain, and a crosslinking agent in combination; JP-A-64-564, JP-A-63-220149, JP-A-63-220148, JP-A-1-280761, JP-A-1-116643 and JP-A-1-169455 disclose a technique using a resin having a low molecular weight (a weight average molecular weight of from 1.times.10.sup.3 to 1.times.10.sup.4) and a resin having a high molecular weight (a weight average molecular weight of 1.times.10.sup.4 or more) in combination; and JP-A-1-211766 and JP-A-2-34859 disclose a technique using the above low molecular weight resin and a heat- and/or photo-curable resin in combination. These references disclose that, according to the proposed techniques, the film strength of the photoconductive layer can be increased sufficiently and also the mechanical strength of the light-sensitive material can be increased without adversely affecting the above-described electrostatic characteristics achieved by using a resin containing an acidic group in a side chain or at the terminal of the polymer main chain.
However, it has been found that, even in the case of using the above-described resins, when the environmental condition charges severely from high humidity and high temperature to low humidity and low temperature, the use of these resins is insufficient for keeping the stable performance of the electrophotographic photosensitive material.
In particular, in a scanning exposure system using a semiconductor laser beam, the exposure time is longer than the exposure time in a conventional overall simultaneous exposure system by visible light, and also there is a restriction on the intensity of the light exposure. Accordingly, a higher performance is required for electrostatic characteristics, in particular, dark charge retention and light sensitivity.
Furthermore, in the case of employing a scanning exposure system using a semiconductor laser beam for a lithographic printing master plate by an electrophotographic system, when a conventional electrophotographic photosensitive material is used for the practical test, the above-described electrostatic characteristics are unsatisfactory, particularly in that the difference between E.sub.1/2 and E.sub.1/10 becomes large, thereby making it difficult to reduce the residual potential after light exposure, the formation of fog on copied images becomes severe. Also, there is a serious problem in that, when printing is carried out using the master plate formed as an offset master plate, edge marks of cutting appear on the prints.